Grommet for speaker enclosure

ABSTRACT

A resilient grommet for forming an airtight seal in an opening while permitting the airtight passage of an electrical cord through the opening. The grommet provides strain relief for the cord and is provided with a series of ribs to prevent pullout.

United States Patent Donald W. Orlowski Glenview; Donald S. Schroeder,Barrington, lll.

Aug. 12, 1969 May 25, 1971 Ampex Corporation Redwood City, Calif.

Inventors Appl. No. Filed Patented Assignee GROMMET FOR SPEAKERENCLOSURE 4 Claims, 5 Drawing Figs.

US. Cl 174/153, 16/2, 181/31, 248/56, 277/178 Int. Cl H0lb 1 7/30, H04r7/16, F161 5/02 Field of Search 174/65 (G), 152.2, 153 (G); 339/103 (B),106; 277/178;

248/56; 16/2; 179/1 (E), 178--l79; l8l/3l.l

References Cited UNITED STATES PATENTS 2,225,472 12/1940 Franklin ..l74/153(G)UX 2,900,453 8/1959 Cammack 181/3'1 .'1 x 3,043,912 7/1962DeLaney 1s1/31(.1 x 3,229,083 l/l966 George,.lr. ..174/153 0)ux FOREIGNPATENTS 35,345 6/1966 Finland 174/153(G) 824,655 12/1951 Germany....l74/153(G) 837,717 5/1952 Germany l74/l53(G) 1,070,186 6/1967GreatBritain 179/102 Primary Examiner-Laramie E. AskinAttorneys-Anderson, Luedeka, Fitch, Even and Tabin and Robert G. ClayABSTRACT: A resilient grommet for forming an airtight seal in an openingwhile permitting the airtight passage of an electrical cord through theopening. The grommet provides strain relief for the cord and is providedwith a series of ribs to prevent pullout.

Patented Ma 25, 1971 3,580,988

FIG.4

iib; I i 2' IIWEI'IDID DONALD W. DRLDWDKI DONALD D. DOI'IRDIDIR GRO MMETFOR SPEAKER ENCLOSURE The present invention is directed to a grommetsuitable for permitting of a cord or the like through an opening in awall. The invention finds particular application in the field of highquality sound reproduction where it is necessary to provide access to aspeaker enclosure for an electrical cord, carrying operatingrpower forthe speaker, while providing strain relief for the cord and a completeair seal of the opening through which the cord passes into the speakerenclosure.

In the field of sound reproduction, one principle of speaker design hasbeen developed called air suspension. It involves a completely sealedenclosure for mounting the speaker driver or unit. The enclosurecontains only static trapped air and permits essentially no airflow intoor out of the enclosure in the area behind the speaker. The trapped airserves as a linear pneumatic spring which restores the cone to itsequilibrium position after it has been deflected inwardly or outwardlyin response to an audio signal. In order for such an air suspensionspeaker to be operative there should be provided an essentially completeair seal of the enclosure behind the speaker so that a pressuredifferential is established between the air in the enclosure and theambient air whenever the speaker cone moves from its equilibriumposition. This differential operates to restore the speaker cone to itsequilibrium position after each audio signal is received.

While most of the design of such an enclosure is not difficult in orderto affect a seal, the one obvious area for air leakage in the enclosureis the opening for the passage of the speaker cord or wire to theterminals of the speaker. In order to be effective, the sealing meansaround the cord extending through the wall of the speaker enclosureshould provide a completely airtight seal between the opening in thehousing and the cord as well as providing strain relief to avoidshorting or breaking of the cord by bending.

It is an object of the present invention to provide an grommet suitablefor forming a complete air seal between an opening in a wall and a cordpassing through the opening.

It is a further object of the invention to provide a sealing meansadaptable for use with openings in walls of different thickness.

It is another object of the present invention to provide a combined airseal and strain relief for passing a cord through an enclosure wall.

These and other objects of the present invention will become obvious inconnection with the following description and drawings in which: 7

FIG. l-is a side elevational view of a speaker enclosure partially incross section and embodying the present invention;

FIG. 2 is an end view of one embodiment of a grommet of the presentinvention;

FIG. 3 is a side view partially in section of a grommet taken along line3-3 of FIG. 2;

FIG. 4 is afragmentary cross-sectional view of the embodiment of FIG. 2in an enclosure wall; and

FIG. 5 is a fragmentary cross-sectional view of the embodiment of FIG. 2mounted in a second enclosure wall.

In the embodiment illustrated in FIG. 1 a speaker enclosure of the airsuspension variety is shown in side elevation with the nearest sidewallbroken away to show the inside of the enclosure. The enclosure may bemade of any suitable material such as wood and is in the form of arectangular box having a .front wall 12 which contains an opening. 14 inwhich a speaker 16 is mounted. The speaker 16 may be of any conventionalconfiguration and maybe of oval or circular cross section. In order toform a seal with the front wall a resilient gasket I8 is providedbetween the rim of the speaker cone and the inside of the front wall 12.Fastening of the speaker to the front wall may be accomplished by anyconventional means such as screws which compress the rim of the speakercone against the resilient gasket 18 to form a seal. Although only onespeaker is illustrated it is understood that more than one speaker maybe so mounted in the enclosure without departing from the invention. Theremainder of the speaker enclosure is joined at right angle corners andsealed by glueing or other sealing means.

The only remaining inlet for air to enter and exit the enclosure isprovided by an opening or hole 20 in the back wall 21 of the enclosure.

In the illustrated embodiment the opening 20 is positioned on the lowerportion of the backwall as the speaker sits in an upright position,however, it could be located at any point on the backwall or any wall ofthe enclosure. The purpose of the opening in the wall is to permit anelectrical cord 22 to be brought into the speaker enclosure and beconnected to the terminals of the speaker 16. As mentioned earlier, inan air suspension type of speaker system it is necessary that there bysubstantially no access to outside air for the air within the speakerenclosure. The reason for wanting to exclude any movement of air in andout of the speaker unit is that air when confined acts elastically andcompressing of the air results in an increase in pressure. The increasedpressure tends to cause expansion of the inside of the enclosure untilthe air reaches ambient pressure at its original volume. Thus, when thespeaker cone moves inwardly and lowers the internal volume of thespeaker enclosure, the pressure inside the enclosure is raised to alevel above the room pressure outside of the enclosure. As the airwithin the enclosure attempts to equalize itself in pressure with thepressure within the room, it acts as a spring and exerts a force on theentire back surface of the cone of the speaker pushing it back towardthe equilibrium position. In like manner, if the speaker is moved by asignal in a direction outward of the enclosure causing the volume of theenclosure to increase beyond its static condition the pressure withinthe enclosure will become lower than the ambient pressure and a forcewill be exerted on the other surface of the speaker cone by the room aircausing it again to return to an equilibrium position in which thepressure within the enclosure is equal to the ambient pressure outsidethe enclosure.

There is inherently in the speaker cone itself a small amount of leakagewhich permits very slow movement of air through the speaker surface.This low rate of leakage does not affect the air suspension propertiesof the speaker because the movement of the speaker cone in response tosignals from the audio input is of such short duration that the leakagehas no opportunity to occur and has no effect on the dynamic propertiesof the speaker. At the same time this low rate of leakage does permitthe pressure within the enclosure to equalize with the ambient pressurein response to the gradual changes in atmospheric pressure so that instatic condition the pressure within the enclosure is always equal tothe pressure on the outside of the enclosure within the room. Thus,changes in atmospheric pressure do not change the equilibrium point ofthe speaker cone.

In order to assure that a slow rate leakage through the apex of thespeaker cone is the only means for air movement into and out of theenclosure, the opening 20 in the rear wall 21 is provided with a grommet24 which is inserted in the opening 20 and surrounds the cord 22 forminga complete air seal in the opening 20.

Referring now to FIGS. 2 and 3 one embodiment of a grommet of thepresent invention is illustrated. The grommet may be made of anysuitable resilient material such as chlorobutadiene polymer or othertypes of synthetic rubbers. As illustrated the grommet 24 is made up ofan elongate cylindrical body of resilient material and is of circularcross section at all points along its length regardless of changes indiameter. It could, of course, be made oval or some other shape withoutdeparting from the scope of the invention in the event that the opening20 in the housing should for some reason be desired to be other thancircular.

Referring again to FIG. 3 showing the grommet partially in cross sectiontaken along line 3-3 of HO. 2, the body of the grommet is divided intoseveral different areas. The first of these areas is an elongate stem 26of constant circular diameter. The stem 26 is of sufficient length toextend completely through the wall of the speaker enclosure in which thegrommet is to be inserted so as to provide a means for grasping thegrommet to pull it into position during assembly. Since the grommetis'adaptable to several wall thicknesses the stem 26 should be longerthan the thicknesses of the thickest wall in v which the grommet is tobe inserted. The stem 26 is also of a diameter just slightly smallerthan the opening in the wallof the housing into which it is to beinserted so that it may be freely inserted without any friction.

A series of ribs 28 extending circumferentially around the grommet areprovided at one end of the stem 26 and define a larger diameter portionof the grommet. Each rib 28 is provided with a sloping face 30 and aperpendicular face 32. The first sloping face 30 begins at the terminalpoint of the stem 26 and is of equal diameter with the stem at thatpoint. It extends outwardly to a larger diameter in a directionslopingaway from the stem 26. The perpendicular face 32 which is perpendicularto the common central axis of the entire grommet extends outwardly fromthe surface of the main body of the grommet until it intersects thesloping face 30 to form a sharp rib 28. The adjacent rib then beginswith another sloping face which intersects the smallest diameter of theprevious perpendicular face 32 at approximately the same diameter as thediameter of the stem 26. In the illustrated embodiment five ribs areshown in succession each having the same outer diameter formed by theintersection of the perpendicular face 32 and the sloping face 30 andeach having the sloping face 30 extending in the same direction outwardand away from the stem 26. The actual number of ribs employed is amatter of choice; however, employing five ribs as illustrated provides asufficient number of ribs to adapt the grommet to several wallthicknesses as will be explained hereinafter.

After the last rib 28, the grommetis provided with an area of constantdiameter 34 larger than the diameter of the stem 26 and approximatelyequal to the diameter of the opening 20. The area of constant diameter34 is interrupted in the illustrated embodiment by three raised portions36 of generally semicircular cross section extending peripherally aroundthe grommet at equally spaced intervals along the constant diameterportion 34. The outer diameter of the raised portions 36 is larger thanthe diameter of the opening in the wall of the speaker enclosure.Therefore, when the grommet is inserted in the opening in the'enclosurewall the raised portions 36 are compressed and form an air seal with theopening 20. At the same time the compression of the raised portionscauses the grommet to form a second seal around the cord 22 as will beexplained hereinafter. Finally, the grommet is provided with a circularflange 38 Y which extends radially beyond the remainder of the grommet.The purpose of the flange 38 is to provide an abutting surface on theouter surface of the wall at the opening 20 thereby preventing thegrommet from being pulled through the opening 20 when it is inserted. Italso functions to assist in the air sealing of the opening 20. The diameter of the flange 38 is substantially greater than the opening 20 toinsure that the grommet will not be pulled through the opening and intothe enclosure during assembly or afterward.

As best seen in FIGS. 2 and 3 the grommet is provided with an opening 40along its central axis which extends with constant cross section fromthe flange end of the grommet to the opposite end of the stem 26. Thisopening provides the passage for the cord to be inserted into thespeaker and attached to the terminals. In the illustrated embodiment theopening 40 is formed by two cylinders each having equal radius andhaving their centers spaced slightly less than a diameter apart. Theresulting cross section seen in FIG. 2 is that of a FIG. 8 and isadapted to receive a double lead cord 22 such as shown in FIG. 4. Ifother shapes of cord are to be employed the central opening 40 shouldhave the cross section of that cord.

The central opening 40 is dimensioned to be slightly larger thanthe'dimensions of the cord to be received so that the cord may be easilyinserted therein. The central opening is also provided, at the end ofthe grommet having the flange 38, with a chamfer 42 to assist theinsertion of the cord into the opening.

The operation the grommet 24 can best be seen by reference to FIGS. 4and 5. The cord 22 is first inserted through the central opening 40.Since the opening is of slightly larger dimension than the cord there islittle friction and the cord can be pushed through the grommet. Thegrommet and cord are then inserted through the opening 20. In performingthis operation the stem 26 can be easily grasped and pulled into theenclosure causing the remainder of the grommet to be pulled through theopening 20. The grommet is pulled into the opening 20 until the flange38 abuts the outer surface of the backwall 21. During the insertionoperation the resilient ribs 28 are compressed in order to pass themthrough the opening 20. As each rib passes through the opening and intothe enclosure it returns to its original shape and provides a stop bymeans of the perpendicular face 32 which resists the pull out of thegrommet in the opposite direction. In its inserted position as shown inFIG. 4 with the thinnest housing wall for which it is designed all ofthe ribs 28 are within the enclosure with the perpendicular face 32 ofthe final rib just abutting the inner surface of the wall 21. The threeraised portions 36 remain within the opening 20 and provide the requiredsealing action by being compressed against the periphery of the opening20. The compression of the raised portions 36 causes the area within thegrommet just below each of the raised portions to also be compressedinto contact with the outer surface of the cord 22 forming a second sealtherewith. Thus, the entire opening is sealed to air movement both atthe passage of the cord and at the passage of the grommet through theopening 20.

FIG. 5 illustrates the grommet inserted into a thicker wall 21a. In thisapplication the same grommet is used and is inserted into the wall inthe same fashion as described above with reference to FIG. 4. In thisenvironment, however, the final rib 28 does not enter the enclosure butremains in its flexed position with the opening 20 to assist the threeraised portions 36 in forming the air seal between the grommet and theopening 20. As in the application of FIG. 4 the primary seal in theopening 20 is still provided by the compression of the raised portions36. In addition, the compression of the final rib assists in thecompression of the opening 40 onto the wire to form the second seaL'Asin the application of FIG. 4 the first perpendicular face 32 within theenclosure, in this case on the next to last rib, is positioned againstthe inner surface of the wall 21a to prevent pull out of the grommet.

It can therefore readily be seen that the grommet shown is adaptable toseveral wall thicknesses by having successive ribs remain in compressionwithin the opening while retaining the feature that the perpendicularface 32 of one of the ribs is always adjacent the inner surface of thewall to prevent pull out.

If for a particular application it is felt that prevention of cord pullout from the grommet is necessary beyond that provided by the squeezingaction of the grommet on the cord of the opening 20 a knot can be tiedin the cord 22 just inside the end of the stem 26 and the cord can bepulled slightly outward so that the knot locks within the resilientopening 40 at the end of the stem 26. This action does not assist ordetract from the sealing effect but merely provides a better anchor forthe cord against pull out.

The grommet described above provides the speaker enclosure with severaldesirable'features simultaneously. First, it forms an airtight sealnecessary to the operation of an air suspension speaker system whilepermitting the lead cord to be inserted through the wall of the speakerenclosure. Secondly, it provides good strain relief for the cord as itpasses through the opening to avoid shorting caused by sharp bendsagainst the edge of the opening 20. It is further assisted at the outerend of the grommet by the chamfer 42 which provides a transition areafor the cord 22 as it enters the central opening.

In addition to these two advantages in the operation of the speaker unitthe grommet also provides features of adaptability and ease of assembly.The adaptability is provided by the series of ribs which permit thegrommet to be inserted in walls of varying thicknesses. The ease ofassembly is provided by the stem 26 which is designed to be of a smallerdiameter than the opening 20 and can be readily inserted and pulledthrough from the inside to avoid the bun ching and twisting caused bytrying to push the grommet into the opening 20. Accordingly, the presentinvention'has provided a versatile low cost strain reliever whichprovides an airtight seal for conducting a lead beyond the outer surfaceof said second cylindrical portion,

a central opening extending through the entire length of said grommetparallel to the common axis, said central opening being of uniform crosssection and adapted to receive an electrical cord extending through saidgrommet.

2. A grommet defined in claim 1, further comprising a resilient flangeintegrally formed at the end of said second cylindrical portion remotefrom said first cylindrical portion, said flange being of largerdiameter than said second cylindrical portion and adapted to provide anabutting surface when said grommet is positioned in an opening to form aseal.

3. A grommet defined in claim 1, further comprising an elongate stemintegrally formed and coaxial with said first cylindrical portion, saidstem being of smaller diameter than said first cylindrical portion andextending from the end of said first cylindrical portion remote fromsaid second cylindrical portion.

4. A grommet defined in claim 1, wherein said circumferential ribscomprise a sloping face and a perpendicular face, said sloping faceextending radially outward and toward said second cylindrical portion,said perpendicular face extending radially outward perpendicular to theaxis of said cylindrical portion and intersecting said sloping face todefine a circular edge.

1. A resilient grommet for forming an airtight seal for wires passingthrough an opening, said grommet comprising a first cylindrical portionprovided with a plurality of axially spaced circumferential ribs, asecond cylindrical portion coaxial and integral with one end of saidfirst cylindrical portion, said second cylindrical portion beingprovided with a plurality of axially spaced circumferential rings, saidrings extending slightly beyond the outer surface of said secondcylindrical portion, a central opening extending through the entirelength of said grommet parallel to the common axis, said central openingbeing of uniform cross section and adapted to receive an electrical cordextending through said grommet.
 2. A grommet defined in claim 1, furthercomprising a resilient flange integrally formed at the end of saidsecond cylindrical portion remote from said first cylindrical portion,said flange being of larger diameter than said second cylindricalportion and adapted to provide an abutting surface when said grommet ispositioned in an opening to form a seal.
 3. A grommet defined in claim1, further comprising an elongate stem integrally formed and coaxialwith said first cylindrical portion, said stem being of smaller diameterthan said firSt cylindrical portion and extending from the end of saidfirst cylindrical portion remote from said second cylindrical portion.4. A grommet defined in claim 1, wherein said circumferential ribscomprise a sloping face and a perpendicular face, said sloping faceextending radially outward and toward said second cylindrical portion,said perpendicular face extending radially outward perpendicular to theaxis of said cylindrical portion and intersecting said sloping face todefine a circular edge.